The present invention relates to a flying-type composite magnetic head for use in a magnetic disk drive in such a manner that it is slightly floating over a magnetic recording medium, and more particularly to a flying-type composite magnetic head having not only excellent recording-reproduction characteristics but also good flatness in its air-bearing surface.
As magnetic heads used for writing and reading information in magnetic disk apparatuses, flying-type magnetic heads as shown in U.S. Pat. No. 3,823,416 and Japanese Patent Publication No. 57-569 are widely used. Such a flying-type magnetic head is constituted by a slider, a tail end of which is provided with a magnetic gap, and the overall slider body is constituted by an oxide-type magnetic material with high permeability.
The flying-type magnetic head is in light contact with a magnetic disk by a spring force when the magnetic disk is stationary, but when the magnetic disk is rotating, a flow of air over the magnetic disk exerts an upward force to a lower surface of the slider, whereby the magnetic head floats over the magnetic disk. When the magnetic disk starts to rotate or stops, the magnetic head comes into sliding contact with the magnetic disk. The contact condition of the magnetic head with the magnetic disk when the magnetic disk is stopped will be explained in detail. First, the flow of surface air becomes gradually slow when the rotation speed of the magnetic disk is reduced. And when the magnetic head loses its floating force, it collides with the disk surface and jumps up by its reaction and then falls onto the disk surface again. Such movement is repeated and the magnetic head slides on the disk to finally stop. Accordingly, the magnetic head should withstand shocks at the time of start and stop, and such characteristics are sometimes called CSS characteristics [contact start stop characteristics].
Flying-type magnetic heads conventionally were constituted by ferrite which is an oxide-type magnetic material with high permeability have relatively good CSS characteristics. However, the ferrite has a small saturation magnetic flux density, so that sufficiently high recording densities cannot be achieved to recording media having high coercive forces. Specifically, even with Mn-Zn ferrite having a relatively high saturation magnetic flux density Bs, its Bs is at most 5000 G or so.
It was then found that to achieve Bs of 8000 G or more, a magnetic head is desirably provided with a thin magnetic metal layer in its magnetic gap. For instance, Japanese Patent Laid-Open No. 58-14311 proposes a flying-type magnetic head composed of ferrite and provided with a magnetic metal layer with high saturation magnetic flux density only in a magnetic gap portion thereof. However, in this magnetic head, a magnetic transformation part has large inductance after provided with coil windings, so that it has low resonance frequency. This means that it is disadvantageous in recording and reproducing at high frequency. Here, the large inductance is due to the fact that the overall magnetic head is composed of a magnetic material. Accordingly, to achieve low inductance, a magnetic, circuit should be made small. From this point of view, U.S. Pat. No. 3,562,444 discloses a flying-type composite magnetic head in which a magnetic core is embedded in and fixed to a non-magnetic slider, without constituting the entire magnetic head with a magnetic material.
Further, the present inventors proposed in Japanese Patent Laid-Open No. 61-199219 a flying-type magnetic head in which a magnetic core is embedded in a non-magnetic slider.
It has been found from the above that to obtain a flying-type composite magnetic head having good recording characteristics to high-coercive force recording media and small inductance, a magnetic core should be constituted by a Mn-Zn ferrite substrate with a high saturation magnetic flux density Bs and coated with a thin magnetic layer having high Bs in its magnetic gap portion, and such magnetic core should be embedded in a non-magnetic slider. An example of such magnetic heads is shown in Japanese Patent Laid-Open No. 60-154310 by the present inventors.
Further, Japanese Patent Laid-Open No. 61-199217 proposed a magnetic head in which a magnetic gap portion of a magnetic core is in an X-shape. In this X-shaped magnetic gap, however, each core piece has a sharp tip portion coated with a high-Bs magnetic thin layer and ground in parallel for defining the magnetic gap. Accordingly, to obtain a desired track width, the high-Bs magnetic thin layer should have a somewhat large thickness.
Further, to obtain a high-performance flying-type composite magnetic head, it is important to maintain a stable floating height in the course of the rotation of a magnetic disk.
While the magnetic disk is rotating, the air on the surface of the magnetic disk also moves to exert an upward force to a lower surface of the slider. Accordingly, the magnetic head floats from the magnetic disk during the rotation of the magnetic disk. The distance of the magnetic head from the magnetic disk is called a floating height, and the floating height is decreasing year after year because of the increase in recording density of magnetic disk apparatuses. According to Computer Strage Industry Service [Section of Rigid Disk Drive] issued by Dataquest, 1984, pp. 2.2-6, the floating height has reached to 10 microinches [0.25 .mu.m]. To keep such a submicron floating height stable during the rotation of the magnetic disk, an air-bearing surface of the magnetic head should have good flatness. Since the floating of the magnetic head is obtained by an air flow passing through a gap between the floating surface of the magnetic head [lower surface of the slider] and an upper surface of the recording medium, stable floating cannot be achieved without good flatness of the floating surface of the magnetic head.
In the case of a magnetic head disclosed in U.S. Pat. No. 3,823,416, since the air-bearing surface acting to cause the floating of the magnetic head is constituted by a single body made of Ni-Zn ferrite or Mn-Zn ferrite, good flatness is easily achieved. However, in the case of a composite magnetic head obtained by embedding a magnetic core in a slit of a non-magnetic slider, fixing the magnetic core with glass and then grinding and polishing its air-bearing surface, special attention should be paid to improve its flatness. This is due to the fact that it is extremely difficult to grind the air-bearing surface to such an extent that the magnetic core and the bonding glass are completely in the same plane as the non-magnetic slider.
Thus, the desired characteristics of a magnetic head for use with a magnetic disk are [1] sufficient recordability to high-coercive force media, [2] low inductance, [3] high reproduced output without causing undulation due to extreme strain in a high Bs magnetic layer, and [4] excellent CSS characteristics.